Communications between deaf persons or the hearing impaired have been previously accomplished by telecommunication systems using voice grade telephone lines connecting two terminals of the system. In one such telecommunication system, a telegraph system utilizes two Teletypewriters as the transmitting and receiving stations for connecting these two terminals for carrying signals over ordinary telephone lines. U.S. Pat. No. 3,507,997 issuing to R. H. Weitbrecht on Apr. 21, 1970 is an example of such a telegraph system for enabling communications between the hearing impaired. The system includes a separate keying unit, a transmitter unit, receiver unit and teleprinter for each of the stations in a communications network connected by ordinary telephone circuits. The system is not designed to enable a user to readily transport the system by carrying it on his person, and the Teletypewriter produces a hard copy of the transmitted text which may disturb the others within the vicinity of the teletypewriter by the resulting noise.
Another type of telecommunication system for the hearing impaired includes a separate keyboard entry terminal for encoding an operator's message and an ordinary television receiver connected to the terminal to display both the message as it is typed as well as the message as it is received. The encoded message is transmitted by an acoustic coupler for coupling the telephone receivers to transmit the signals over ordinary voice grade telephone lines. U.S. Pat. No. 3,746,793 discloses such a system, and U.S. Pat. No. 3,896,267 discloses an improvement to that system by means of a switch which enables the encoded keyboard entries to be transmitted in either Baudot or ASCII code.
Yet another approach to enable communications between the deaf or hearing impaired over telephone lines has been accomplished by use of the twelve- or sixteen-key pushbutton telephones as the means for coding and transmitting messages containing alphanumeric data to another terminal of the system. U.S. Pat. No. 3,870,821 discloses such a system, but the system requires a separate printer for providing a hard copy of a message on tape, as well as requiring the user to learn a special code requiring the depression of several keys to generate a single alpha or numeric character. U.S. Pat. Nos. 3,675,513 and 4,012,599 disclose additional telephone communication systems for the deaf which require the use of special codes for the keys of a pushbutton telephone for generating characters to be transmitted to another terminal of the system. In addition to enabling communications between the hearing impaired, keyboard encoded communications terminals have also been provided to enable a user to access a central computer facility and transmit data to the computer over voice grade telephone lines.
A need has thus arisen for an improved, easier to operate portable communications terminal in a telecommunications system for transmitting and receiving messages over ordinary telephone lines for improving communications between deaf and hearing impaired and for improving the transmission and reception of data to a remote central data processing facility for a portable terminal.